Re: [Xen-devel] [PATCH 2/7] xen/arm/vgic-v2: Ignore write to GICD_ISACTIVERn registers

[Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>]

Hi,


On Thu, Apr 12, 2018 at 1:31 AM, Stefano Stabellini
<sstabellini@xxxxxxxxxx> wrote:
> On Wed, 11 Apr 2018, Julien Grall wrote:
>> On 11/04/18 14:19, Mirela Simonovic wrote:
>> > Guests attempt to write into these registers on resume (for example Linux).
>> > Without this patch a data abort exception will be raised to the guest.
>> > This patch handles the write access by ignoring it. This should be fine for
>> > now because reading these registers is already handled as 'read as zero'.
>>
>> I think this patch is wrong. It is not mandatory for the guest to write
>> exactly the same value as read. Assuming the guest will always write 0, then
>> what you want to do is checking the write is actually 0. In that case you can
>> ignore it. For all the other case, you should still fail.
>
> Yes indeed, and that should be fine because GICD_ISACTIVER is already
> implemented as read_as_zero.
>

Thanks, I fixed this (will be submitted in v2 series).

>
>> >
>> > Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>
>> > ---
>> >   xen/arch/arm/vgic-v2.c | 3 +--
>> >   1 file changed, 1 insertion(+), 2 deletions(-)
>> >
>> > diff --git a/xen/arch/arm/vgic-v2.c b/xen/arch/arm/vgic-v2.c
>> > index 646d1f3d12..b088376ed0 100644
>> > --- a/xen/arch/arm/vgic-v2.c
>> > +++ b/xen/arch/arm/vgic-v2.c
>> > @@ -484,11 +484,10 @@ static int vgic_v2_distr_mmio_write(struct vcpu *v,
>> > mmio_info_t *info,
>> >           return 0;
>> >         case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
>> > -        if ( dabt.size != DABT_WORD ) goto bad_width;
>> >           printk(XENLOG_G_ERR
>> >                  "%pv: vGICD: unhandled word write %#"PRIregister" to
>> > ISACTIVER%d\n",
>> >                  v, r, gicd_reg - GICD_ISACTIVER);
>> > -        return 0;
>> > +        goto write_ignore_32;
>> >         case VRANGE32(GICD_ICACTIVER, GICD_ICACTIVERN):
>> >           printk(XENLOG_G_ERR
>> >
>>
>> --
>> Julien Grall
>>

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel